As far as I understood it, you are right technically. However, each iTunes account can only be tied 10 devices, 5 of which can be PCs. So in practice, that is 5.

iTunes. Not the Mac App Store. You're misplacing the limitations. You cannot authorize iTunes on more than 5 computers (unlimited iDevices, however). You can, however, authorize the Mac App Store on an unlimited number of Macs.